The present work investigates experimentally the effect of H2O vapor on the removal of NO at elevated temperatures. Breakdown voltage, discharge characteristics and NO removal efficiency were studied under various conditions of water vapor content. The experimental results indicate H2O can greatly enhance the NO removal efficiency from a NO/O-2/N-2/C2H4/H2O system, but the breakdown voltage increases as the relative humidity of the gas increases. Moreover, the effect of temperature on NO removal at a relative gas humidity of 30 % was analyzed. With an increase in temperature, E/N increased, producing more active species and energetic electrons; electron detachment also became significant at high temperature and the rates of major reactions were promoted, intensifying the conversion of NO.